The invention relates generally to wastewater treatment and particularly to treatment of effluent containing dyestuffs and other organics, inorganics, particulates and dissolved materials exiting a garment stonewashing or similar process.
Treatment of wastewater effluent from industrial processing has long been the subject of technical inquiry and practical application due not only to the continuing need for clean water but also due to the cost of using water in process water makeup situations and particularly those situations requiring clean water for process makeup. While the present methodology can extend to water reclamation and recycling in a number of industries including food processing, electronics manufacturing, metals plating, pulp and paper, etc., the present methodology is particularly useful for reclaiming and recycling water from the effluent of textile and dye plants and particularly in the processing of stonewashed and/or sandblasted garments wherein detergents, enzymes, fibers, surfactants, silicates, etc., must be removed from processing effluent with the treated water being sufficiently clean to allow recycle. Expensive water dumping fees are thus avoided by the ability to reuse process water according to the invention. In the treatment of garments and similar items by stonewashing and the like, large amounts of water are necessary to form the process medium in which cotton xe2x80x9cbluejeansxe2x80x9d and garments formed of blends including polyester/cotton blends, rayon/cotton blends, etc. are treated. In typical stonewashing processes, an abrasive such as pumice is used in combination with detergents, bleach and enzymes to alter the color and texture of garments, these garments being processed in industrial washing machines with the treating materials which can further include dyestuffs, treatment periods varying from minutes to hours. A common practice in the prior art has been to simply discharge the effluent from such processing directly into city wastewater systems. The continuing rise in the cost of water for initial process water makeup and the institution of sewer discharge fees causes prior art discharge practices to become prohibitively expensive. The need to recycle water from processing effluent has therefore become quite apparent to the garment processing industry as well as industry in general.
Examples of prior art teachings intended particularly for removal of dye materials from wastewater effluents are provided inter alia by Weber in U.S. Pat. No. 5,360,551, this patent removing color from dye wastewater through acidification and subsequent use of a cationic flocculent. An optional step in the Weber process is the addition of a reducing agent to produce a desired oxidation-reduction potential, the reducing agent being an alkali metal hydrosulfite, an alkaline earth hydrosulfite, mixtures thereof or combinations of an alkali metal bisulfite, an alkaline earth bisulfite, an alkali metal borohydride and mixtures thereof. In U.S. Pat. No. 5,611,934, Shepperd et al remove dye from process water effluent through treatment of the effluent with a reducing agent, adjustment of pH, treatment with a charged neutralization mixture and flocculation after a second pH adjustment. The particular charge neutralization mixture includes an aluminum salt and a cationic polymer consisting of a copolymer of acrylamide with a cationic monomer such as methacryloylethyltrimethylammonium halide and further including organic wherein the mixture exhibits a Zeta potential of 15 millivolts. Flocculation agents according to Shepperd et al include anionic polymers such as acrylic acid/acrylamide copolymers and non-ionic polymers such as polyacrylamides. Further teachings of wastewater treatments for removal of organics include U.S. Pat. Nos. 5,529,696 to Tibbits; 5,529,697 to Braasch; 5,529,698 to Timmons and 5,529,699 to Kuole, the Kuole patent particularly describing flocculating agents used in wastewater treatment processing. Grant et al, in U.S. Pat. No. 5,330,658, utilize precipitation and flocculation techniques to remove contaminents from wastewaters and particularly disclose an acidification step for removal of oxidizing agents.
Wastewater treatment according to the invention is particularly intended to remove color, to lower levels of TBS, TSS, BOD and COD in order to allow recycle of process water with resulting savings in makeup and disposal costs. The processes of the invention are particularly suited to treatment of waste-water effluent issuing from garment stonewashing and similar treatment processes. In such processing, wastewater effluent containing detergents, enzymes, fibers, surfactants, silicates, dyestuffs and particulates are treated to allow reclamation of greater than 95% of water originally used for process water makeup. The present processes remove all cotton lint, synthetic fibers, dissolved silica and solid particulates from effluent and further remove bleach, coloring from dyes either added during garment processing or removed from garments by processing, such coloring typically being black, green, red, blue and the like. The present methodology also allows removal of large quantities of soluble surfactants while lowering BOD, DOD, TSS and TBS levels. Suspended fibers, solids and colored materials are further removed in order to render a treated effluent reusable for process water makeup, reuse being possible many times over before a need exists to discharge major amounts of water originally used for makeup purposes. The present methodology can be practiced inexpensively, the physical system necessary for practice of the methodology also being inexpensive to fabricate and operate.
The invention provides methodology and system architecture intended for treatment of wastewater emanating from industrial processes particularly including garment washing processes which can involve removal from a garment of at least a portion of a dyestuff originally applied to the garment. The invention particularly intends the treatment of wastewater effluent from a garment stonewashing process such as the stone-washing of xe2x80x9cjeansxe2x80x9d which can include the removal of dyestuffs from the garment and/or the replacement of dye or color to the garment, the processes of the invention being intended to remove dyestuffs and other organic materials, lint, fibers, silicates and particulate solids inter alia from a stonewashing wastewater effluent in order to render the wastewater or effluent reusable in a stonewashing process or the like. A particular intent of the invention is the removal of materials from the wastewater effluent,which materials were employed for treatment of garments in the process producing the wastewater effluent, such materials including detergents, enzymes, surfactants, silicates and abrasive particulates such as pumice and the like. Processing according to the invention lowers levels of TSS, TDS, BOD and DOD so that water is reclaimed for process water makeup and/or discharge.
In a preferred embodiment of the invention involving the treatment of a wastewater effluent from a xe2x80x9cjeansxe2x80x9d stonewashing process, the wastewater effluent can optionally be filtered prior to subsequent chemical treatment. Since the present processes envision continuous flow treatment of effluent of only a few gallons and up to millions of gallons daily, initial filtration may be waived as long as any particulate material which might be removed by initial filtration is not converted to a dissolved material by subsequent chemical treatment whereby said nearly dissolved material would be difficult to remove by such subsequent chemical treatment. Initial filtration can be effected by passage of the wastewater effluent through a shaker with a mesh size of from 5 to 120 microns to remove large bits of pumice or similar abrasive and any other contaminants which are large enough to be trapped by filtration.
Preferred processes according to the invention include the step of acidification subsequent to optional initial filtration, it being the intent to produce a pH in the effluent of between 2 and 6. Sulfuric acid is the preferred acidifying agent. The acidification step liberates chlorine which may be present in the system in order to prevent the formation of chloride salts which would be more soluble than salts intended to be formed during subsequent chemical treatment. Chemical treatment after the acidification step involves formation of relatively insoluble salts in order to facilitate removal of dissolved materials from the wastewater effluent. It is desirable according to the invention to reduce the presence of salts containing chlorine which can interfere with subsequent clarification steps. Caustic soda is also used for pH control and/or adjustment after the acidification step.
A temperature of approximately 40xc2x0 F. to 140xc2x0 F. should be maintained in the wastewater effluent in order for chemical treatment to proceed at a reasonable rate. Preferred temperatures are between 60xc2x0 F. and 80xc2x0 F. Higher temperatures can adversely affect solubilization and can cause the formation of complexes or flocculation within the wastewater effluent.
The acidified wastewater effluents further treated according to the invention by passage of the effluent in contact with a treatment paste primarily formed of magnesium hydroxide and activated carbon. Activated carbon or activated charcoal is used for removal of color and organics from the effluent as well as other organic compounds which may be present in the effluent. Magnesium hydroxide is present in order to form insoluble magnesium salts as the wastewater effluent flows in and around the paste formed of the magnesium hydroxide and activated carbon. A portion of the paste can be cycled to a subsequent settling tank for further reaction with the waste-water effluent.
The insoluble magnesium salts can be removed by settling or filtration prior to introduction of an iron sulfate either singly or in combination with carbonates, lime, alum, ferric chloride, ferric sulfate and sodium aluminate, these materials being used to precipitate other ionic materials from the solubilized state,which other ionic materials were not removed by the magnesium treatment.
Flocculation through use of an ionic flocculent such as a highly water soluble polyacrylonitrile polymer can then take place. A polyacrylamide can be used to cause flocculation of materials which have not been absorbed by the activated carbon or precipitated by the precipitating agents previously added to the wastewater effluent. Depending upon the type of effluent to be treated, flocculents such as amines, polyacrylamides, ammonium chlorides or polydimethylammonium chlorides can be used as flocculating agents.
Settling can be employed for removal of precipitated materials and flocculated materials with filtration being employed as necessary. The resulting high purity water can be recycled to a stonewashing process or other wastewater effluent-producing process or can be discharged as a system effluent which meets applicable environmental regulations. The same water can be treated up to thirty times by the present processing prior to a need for discharge.
System architecture can include shaker filtration apparatus capable of the initial filtration step described above. Filtration can be accomplished through the use of filter press apparatus utilizing diatomaceous earth. Further, bag filters can also be employed as well as other filtration apparatus known in the art. Tanks used for acidification as well as other chemical treatment including clarification can be tanks having conical lower portions which facilitate precipitate removal or settling. The physical system of the invention can be automated to include pH monitoring and control as well as control of all plumbing including pumps and the like which involve charging of treating materials into the wastewater effluent.
While the present methodology is described herein primarily in reference to treatment of a wastewater effluent from a jeans or garment stonewashing process, it is to be understood that the present methodology can be employed in food processing, particularly beef slaughterhouse waste processing, pulp and paper processing, railcar and locomotive washing, metals and plating, mining, semiconductor and electronics manufacturing and other textile and dye applications.
Accordingly, it is a primary object of the invention to provide wastewater treatment processes and preferred systems for practice of the processes which are intended to remove particulates and dissolved materials contaminating such effluents in industrial applications including garment stonewashing, beef processing, electronics manufacturing and the like.
It is another object of the invention to provide wastewater treatment processes and preferred systems for practice of the processes which are particularly intended to remove particulates, dyestuffs and dissolved materials as well as organics from garment stonewashing and similar processes to allow continuing recycle of relatively pure water from the wastewater effluent for new process water makeup.
It is a further object of the invention to provide wastewater treatment process and apparatus wherein at least one precipitating agent formed into a paste with an absorbent such as activated carbon or charcoal is caused to contact waste-water effluent in order to remove the contaminants from solution and place said contaminants into a form readily removed by physical removal processes.
Further objects and advantages of the invention will become more readily apparent in light of the following detailed description of the preferred embodiments.